Polytechnic Association. 615 



twenty-five minutes. Where templates or patterns of metal are used, 

 the blows of the impinging sand soon cause the metal to curl up as 

 though under the blows of a planing hammer, even hardened steel 

 being affected in this way. Fine lace will leave its design upon the 

 surface of glass most perfectly, and the lace patterns cut in paper 

 make excellent work. 



In examining the action, of the sand-blast upon the glass with a 

 microscope, it is found to have a more uniform surface than is left by 

 the rubbing or grinding process to accomplish the same end. At the 

 point cut by the sand in the blast a reddish light is seen, caused 

 probably by the crushing or cutting action of the sharp parades. It 

 may be suggested that the dust from the cut materials will be very 

 injurious to the workmen employed about the machines; but this can 

 be easily obviated by using the sand and dust as in the smaller 

 machines, or where a high-pressure blast is used, as is now in operation 

 at the fair, a fan blower can draw the spent material from the sur- 

 face of the work and keep the stream constantly returning to the 

 hopper. 



Mr. Weir exhibited specimens of work done by this process at the 

 fair of the American Institute. 



Mr. J. K. Fisher inquired whether the process could be applied for 

 drilling stone. 



Mr. Weir stated that it could be used for splitting stone, by cutting 

 a groove into which wedges could be driven. 



Mr. Disturnell inquired whether it could be used for dividing 

 masses of copper. 



Mr. Weir — No, sir; it would cut a diamond sooner than copper. 

 Copper is so soft that it is a good material for a template. 



Dr. Feuchtwanger, conceding the fineness of the photograph etched 

 by this process, said that he could do it equally well in a quarter of 

 a minute by hydrofluoric acid. 



Mr. Weir — It took but six or eight seconds to do this, with a press- 

 ure of only about two ounces to the inch. 



Mr. Fisher — Can glass be depolished for windows by this process, 

 economically ? 



Mr. Weir — It is a very simple thing to do, but I do not know how 

 much it would cost. 



Mr. Disturnell — I was in hopes this could be used for disintegrat- 

 ing copper, or dividing the masses, which is now done by a very expen- 

 sive process. If human skill can invent any process for disintegrating 

 those masses, it will be invaluable. 



